1. Field of Invention
The present invention relates to an illuminating device and a luminance switching device thereof, and more particularly to a luminance switching device with a built-in memory unit for providing a multi-stage switching of various illuminating devices.
2. Related Art
In recent years, light emitting diodes (LEDs) has been widely used in daily life, for example, in monitors, home appliances, electronic components for vehicles, and lighting lamps. Taking domestic lighting lamps as an example, a conventional domestic lighting lamp usually has a plurality of bulbs, and when a user wants to change the luminance state of the environment, a changeover switch is used to sequentially switch the plurality of bulbs in multiple stages according to a set value, so as to turn off the bulbs. For example, when the changeover switch is just turned on, all of the bulbs are in a turn-on state. When the changeover switch is turned off and then turned on again, at least one bulb is in a turn-off state, which results in the weakening of luminance of the light emitted by the entire lighting lamp. When the changeover switch is turned off and then turned on again, at least one bulb that is in the turn-on state in the previous stage assumes the turn-off state. Thus, the luminance of the lighting lamp can be switched in multiple stages. However, when the bulbs of the lighting lamp are replaced by LEDs, as the unit number of LEDs required in the bulbs is large, the luminance of the light emitted from the entire lighting lamp will be uneven if the LEDs of the lighting lamp are turned off sequentially according to the operating mode described above.
In order to solve the aforementioned problem of uneven luminance of the devices using the LEDs as the light sources, U.S. Pat. No. 6,344,641 has disclosed a control method of a display system using LEDs as a light source. FIG. 1 is a schematic view of a conventional display system. Referring to FIG. 1, the conventional display system 10 includes two LEDs 12A, 12B, a display device 14, and a luminance detecting and control circuit 20 disposed in the display device 14. The display device 14 includes an image display array 18 to display images of the display device 14. In addition, the display device 14 further includes a controller 22 electrically connected to the luminance detecting and control circuit 20, for transmitting a timing and control signal to the luminance detecting and control circuit 20. The two photo-detectors 16A and 16B are aligned with the LEDs 12A and 12B, and are electrically connected to the luminance detecting and control circuit 20 for detecting luminance of the light emitted by the LEDs 12A and 12B respectively.
When the photo-detectors 16A and 16B detect the luminance of the light emitted by the LEDs 12A and 12B respectively, the detected luminance of the light is converted into a current signal, which is then transmitted to the luminance detecting and control circuit 20. At this time, if the luminance of the LEDs 12A and 12B needs to be changed, the controller 22 will output a modulation signal to the luminance detecting and control circuit 20 according to requirements of the user. Then, the luminance detecting and control circuit 20 integrates the signals from the photo-detectors 16A and 16B and the controller 22, and sends a voltage signal to modulate the luminance to be adjusted of the LEDs 12A and 12B respectively. Thus, the luminance control of the light emitted from the LEDs 12A and 12B of the display device 14 is realized.
However, though the luminance detecting and control circuit 20 controls the luminance of the light emitted by the LEDs 12A and 12B individually, the compensation can only be performed according to the insufficient luminance of the LEDs 12A, 12B detected by the photo-detectors 16A, 16B or the luminance to be adjusted. If the user wants to individually adjust the luminance of the light emitted by the LEDs 12A, 12B to luminance of different states, such that the display device 14 uses the LEDs 12A, 12B to show different brightness. As the photo-detectors 16A and 16B are influenced by the light emitted by the neighboring LEDs 12A, 12B, for example, the photo-detector 16A also detects the light emitted by the LED 12B, the object to control the LEDs 12A, 12B to emit light of different luminance cannot be achieved. Moreover, when the display device 14 uses a large number of LEDs, the luminance detecting and control circuit 20 cannot control the light of different luminance emitted by the LEDs in a specific state at the specific state again while prevent the problem of uneven luminance at the same time.